Mirror displays for digital signage or the like applications have been proposed which include a half mirror layer on the viewing surface side of a display device to function as a mirror (for example, see Patent Literatures 1 to 4). Such mirror displays provide images using display light emitted from the display devices and are also used as mirrors in a state of reflecting external light.
The half mirror layer is an optical member with a reflective function, such as a known reflective polarizing plate (e.g., multiplayer reflective polarizing plate). A reflective polarizing plate reflects incident polarized light vibrating at an azimuth parallel to the reflection axis and transmits incident polarized light vibrating at an azimuth perpendicular to the reflection axis. The reflective polarizing plate therefore can transmit light emitted from a display device as display light to the viewing surface side and reflect external light perpendicular to the polarization direction of the display light to the viewing surface side. Such a mirror display including a reflective polarizing plate as a half mirror layer switches between a display mode and a mirror mode based on such a principle.